Retractable shock absorbing strut



Jan. 25, 1949. E. c. WELLS RETRACTABLE SHOCK ABSORING STRUT Filed Dec. 13, 19,44`

Patented Jan. 2.5, 1949 RETRACTABLEy SHOCK ABSORBING STRUT;

Edward C. Wells, Seattle, Wash., `assigner/to Boeing Airplane- Company, a corporation, of' Delaware Application December 13, 1944, Serial No. 568,030

7'Cliaims. (Cl. 244-102) The strut incorporating my invention is particularly useful for application toairplane tail wheel mountings. Y

It has vbeen `customary heretofore to support '778 issued May 3,1932.

cushioning characteristics.

tendedposition.

if such should be necessary.

different types.

strut.

ure 1.

that showni ridge. post to permit: swivelins.

i@ is resisted 'bv the resilience ,of the Shook Strut! The lower end orflmystut is pivoted by a bolt 1.3 tothe upporondjof post I2, and its, upper ondA is supported for swinging about 'a horizontal axis Preferably Ysuch trunnions are airplane tail Wheelsresiliently, anda ltypical construction is shown in Monteith Patent No. 1A,856, byk trunnions Y,i4 located considerably above the frame pivot l. Aprincipal object of my invention is to'provide' substantially directlyabove pivotY Ill, but this a shock absorbing strut which can be connected relationship is not essential, to a ytail Wheel mounting ofthe general type dis- 10 My strut is `not 'only.resilient, but is variable in closed in the aforesaid patent, enabling it to be effective length, so that-'as itisshortened frame retracted within the confines of the airplane iandv Wheel'li carried byit areswung upward fuselage while at the same time preserving vits about Ypivot l0 toretract the Wheel into the posi- Because of its comtion within the fuselage shown inY broken lines in pact arrangement my strut may be substituted Figurevl. directly for. the Iresilient strut in the tail Wheel While the resilient -mechanism incorporated in mountingA of the above patent, with perhaps only the strut may be of diieren't types, and although a slight change in the anchoring structure for the mechanisrnfor varyingthe length of the strut the upper end of the strut. Nevertheless the remay be modified, I prefer that the Vstrut incorsilience of the gear is not reduced appreciably. 20 poratean outer tube."l andnan'inner tube20 dis- -n fact, the shock absorbing qualities of such a posedin telescoping relationship, .as Shown in tail Wheel assembly Yinoorlooratine .mv Strut aro Figure 2,. The uuperondk of such outer tube is almost as goed `when the tai-1 wheelgis'in'a posisecured to trunnions I4 Vso that as the strut is tion'intermediateits extended position and itsV shortened its lowerV end may lswing forward, as retracted kposition as when it is in the fully exshown Vin broken lines in Figure 1. Such telescoping tubes perform thedual ,function of pro- Substitutionofniy strut to permit retraction of tecting the interior mechanism -from dirt, and Y a tail wheel such as shown in the patent does not of relieving the retracting mechanism from any interfere'with the steerable'characteristics ofthe 30 bending loads .to which .the strutfmay be subtail wheel. The construction of the-strut is simjected. i ple, andiitis composed :of fewparts. Althoughv Tube Eilis` drawn'into the open'lower end of light, the structure'is strongy and is protected tube 2 to reduce -the Alengthof the strut by rotaagainstinltration of dirt which/might interfere tion of screw 2l, thefupperend vof which is jourwith its operation.,` The ,-,strut 'may be removed 35' naled in -wall ZZcIOSingfthe-upper end of tube 2. and disassembled readilyfor cleaning lor repair, Endwise movement of the screw is thus prei Vented, whereas irvtslower end'is threaded into The preferred construction -of my strut shown wall r2? closingvthe upper end of the inner tube the drawings may be modied in minor par- 2i! and serving as a nutrVmovablelengthwise of ticulars asmay be required for installations ofv 40 the screw to swing wheel ls-uppoll-ingy frame f The upper end of this .screw projecting through Figure l is a side elevational view of an air. Wall .22 may be rotated by vany onvonient dri-Ve plane tan wheel `installationincorporating my meohanism, suoh'as -beVel-gears'iwdriven by an actuating device, which-may be a motor ora ilex- Fisure 2L is a lorieit 1151111211l `,sectional4 view 45 ible ,Shaft and oranlaoonnectedto rotate shaft through the struttakon -alonsc'line-TE .of Fig- 25 This shaft extends; conoontrioally through one of the trtuirriorlsA .[4150 that'the driving. con A conventional tailA wheellstructuref simi-lar to nection between such `'shaft v4and screw 2l is. not

Patent1;8,5,6,""7.8` mentioned fabove, interruptedby swinging the strut-upon its trunincludes a rigid frame-i oi ldouble wedgel Shape, 50 nions. In all rotatedpositionsof the screwrit acts having a Afor-wardv :horizontal apex; .ridge member as a true rigid strut element tov resist endwise tenpivoted at in to the fuselageyiustinsideits lower sion, compression and bending loads. vThe tubesurface. Thewheel I I has a spindle received in 2 also assists in resisting'bending loads to keep the Vupright post I-2 -iormingtherearward apex the strut straight.

The spindle .is-jou aiedixsutagbly in-thev Within tube i 20 is-.received a second pair of telescopi-ng tubes, including fa relativelyv outer l tube 3 and an inner tube 30. Tube 20 is then actually an intermediate tube, between the covering tube 2 and the shock absorbing mechanism. The upper end of tube is screwed into or otherwise secured to and carried by the upper end Wall 23 of tube 20. Tubes 20 and 3l) thus, in effect, are one integral part and couldbe formed as a single unit ify desired, or tube 30 couldfeven be omitted entirely, although it would be necessary to alter certain features of the contruction in either of such cases. The annular space between tubes 2|l and 30 receives a spring 3| encircling tube 3B and engaged between the end wall 23 of tube 20 and the vinner end of tube 3, which provides resilience for the shock absorber.

splines 32, engaged between the overlapping portions of tubes 3 and 20, prevent relative rotation of these tubes. In the preferred form of my device endwise separation of tubes 3 and' 38 is prevented by the engagement of an inwardly directed ange 33 on the inner end of tube 3 with an outwardly directed ange ,34 on the lower end of tube Movement of tube 3 inwardly relative to tube 20 is limited either by compression of spring 3| to its full extent, or by engagement of the inner end of tube 3 with the end of the splined portion of tube 2|).

The lower end of tube 3 is preferably closed by a removable cap 35. This cap Ycarries strut connecting means,`including lugs 36 apertured for reception of pivot bolt I3 which interconnects the lower end of the strut andthe upper end of frame post I2. Y Y

It will be noted that cap 35 is hollow and that the interiors of tubes 3 and 3i! are unobstructed. All of these cavities are of a size in cross section exceeding the maximum cross sectionof screw 2|, and are aligned with such screw. As shown in Figure 2, when the strut is in its fully extended condition the lower end of screw 2| does not extend appreciably below the end wall 23 of tube 25|. As the strut is contracted to retract the wheel' i| by upward movement of tube end 23, the screw projects axially rst into the interior of tube 33, then into the interior oftube 3, and finally ,perhapsV even into the cavity of cap 35. The provision of a hollow, shock absorbing structure which enables the strut length adjusting means to be housed completely within it, even when the resilient mechanism is under maximum compression, is primarily responsible for the compact arrangement of my strut which enables it to be Vsubstituted directly for a conventional shock absorbing strut which cannot be shortened to retract the tail wheel.

In assemblingY my strut, spring 3| may be inserted into tube 2E) Yand held in place by sliding tube 3 into the lower end of the former tube with the splined structure 32 properly engaged. Tube 3S, if such a tube is used, may then be inserted through the open lower end of tube 3, and while the latter tube is forced inward against the resistance of spring 3| to remove pressure by its ange 33 on iiange 34 of tube 36, such tube may be screwed into the end wall 23 of tube 2) to hold the tubes in assembled relationship. Extension of the spring is then limited by-engagement of the ilanges 33 and 34. Cap 35 may now be screwed into the lower end of tube 3.

When screw 2| is assembled in tube 2 trunnions al may be mounted in their bearings on the airplane structure. After supporting frame I by its pivot ||i, bolt I3 may be inserted to interconnect the strut mounting lugs 36 with. the

upper end Qif frame Pest 12 Theupper and of 4 Y tube 20 may then be started into the lower end of tube 2 and screw 2| rotated to thread it into the internally threaded hole in tube end 23. With the strut parts thus'assembled a stop may be interengaged lbetween tubes 2 and 20, or the rotation or axial travel of screw 2| may be limited, to prevent extension of the strut sufficiently to disengage the'screw and nut during normal movement of the wheel I l to extended position.

It will be evident that the cushioning action of spring 3i Vbetween tubes 3 and 2li is not altered as the length of this strut is changed by shifting tube 23 relative to screw 2|. Consequently the shock Yof contact between wheel II and the lground would be cushioned by the spring 3| even though the wheel were not'in its fully down position. The resilient characteristics of the gear are somewhat better, however, when the wheel is fully extended, becausel in that condition the resilient strut is substantially vperpendicular to a line joining pivots I0 and i3. Any force tending to swing trame I about pvot I0 would therefore act on the strut in direct compression.

When the angle between a line through pivots l@ and i3 and the strut axis is increased, however, as shown inthe broken line position of the parts in Figure 1, force exerted on the frame acts partially to compress the strut and partially in tension on the longer members of frame I. Under emergency conditions, however, -considerable resilience will be aorded even though the strut is not fully extended.

I Vclaim as my invention: s

1. A strut comprising a tube having a closed end, hollow shock absorbing means received in said tube, strut mounting means received in the open end of said tube, engaged with said shock absorbing means, and movable inwardly Vrelative to said tube against the resilience of said shock absorbing means, a screw threaded in the closed end of said tube and projectiblewithin said tube and l'shock absorbing means, and second strut mounting meansengaged with the portion of said screw exteriorly of said tube for movement thereby lengthwise of said tube to reduce the effective length of said strut as said screw is projected into the hollow Voi said shock absorbing means.

2. A strut comprising a, tube havinga closed end, a spiral spring received in said tube and having one end engaged with the closed end thereof, strut mounting means received in the open end of said tube, engaged with the other end of said spring, and movable inwardly relative to said tube against the lresilience of said spring, a screw threaded in the closed end of said tube and projectible within said tube and spiral spring, and second strut mounting means engaged with the portion of said screw exteriorly of said tube for movement thereby lengthwise of said tube to reduce the effective length of said strut as said screw is projected into 'said spiral spring.

3. A strut comprising an outer tube, an inner tube slidably received within said outer tube, means extending axially of said inner and outer tubes generally centrally thereof, interconnecting said tubes and operable to shift them lengthwise relative to each other between extended and contracted positions, resilient means housed in said inner tube, adapted to encircle said tube interconnecting means in contracted relationship of said tubes, and strut mounting means-carried by said inner tube in Vposition for engagement 'with said resilient means to cushion movement tube in a direction toward said outer tube.

screw extending axially of said inner and outery tubes generally centrally thereof, interconnecting said tubes and operable to shift them length- Wise relative to each other between extended and contracted positions, a spiral spring housed in` said inner tube, adapted to encircle said screw in contracted relationship of said tubes, and strut mounting means carried by said inner tube in position for engagement with said spring to cushion movement of said mounting means relative to said inner tube in a direction toward said outer tube.

5. A strut comprising an outer tube closed at one end, an intermediate tube having a closed end slidably received in the open end of said outer tube, a screw extending axially through said outer tube and having one end journaled in the closed end of said outer tube and its other end threaded into the closed end of said intermediate tube, drive means operable to rotate said screw for moving said outer tube and said intermediate tube relatively lengthwise, an inner tube having its open end slidably received within the open end of said intermediate tube for reception of the en-d of said screw when said outer tube and said intermediate tube are in contracted relationship, strut connecting means* carried by said inner tube, and resilient means disposed within said intermediate tube, engaged by said inner tube and yieldable to cushion shocks transmitted to the strut through said connecting means.

6. A strut comprising an outer tube closed at one end, an intermediate tube having a closed end slidably received in the open end of said outer tube, a screw extending axially through said outer tube and having one end journaled in the closed end of said outer tube and its other end threaded into the closed end of said intermediate tube, drive means operable to rotate said screw for moving said outer tube and said intermediate tube relatively lengthwise, an inner tube having its open end slidably received Within the open end of said intermediate tube for reception of the end of said screw when said outer tube and said intermediate tube are in contracted relationship, strut connecting means carried by said inner tube, and a spiral spring disposed within said intermediate tube, engaged by said inner tube and yieldable to cushion shocks transmitted to the strut through said connecting means.

7. A strut comprising a tube, elongated resilient means, received in said tube and having one end engaged therewith, and providing an elongated cavity therein, strut mounting means engaging the other end of said resilient means, and movable lengthwise of said tube against the resistance of said resilient means, second strut mounting means, and an elongated rigid connecting member carrying said second strut mounting means, having a thrust connection with said tube, and movable into the elongated cavity therein said l resilient means to reduce the eiective length of said strut.

EDWARD C. WELLS.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,490,513 Janin Apr. 15, 1924 1,842,776 Bogoslowsky Jan. 26, 1932- 2,213,967 Roche Sept. 10, 1940 2,238,411 Conklin Apr. 15, 1941 

